U.S. national security advisor (1969–1975) and secretary of state (1973–1977); together with President Richard Milhous Nixon, devised and implemented a major reorientation of U.S. foreign policy. Of German-Jewish extraction, Henry Alfred Kissinger was born on 27 May 1923 in Fürth, Germany. He left Adolf Hitler's Germany for New York in 1938 and became an American citizen five years later. After serving in the U.S. Army, Kissinger became a professor of government at Harvard University, publishing his doctoral dissertation, A World Restored (1955), that focused particularly upon the Austrian Prince von Metternich, whom Kissinger admired and in some ways modeled himself upon. He also published a study of U.S. atomic policy for the prestigious Council on Foreign Relations.

Although his intellectual capabilities were highly respected, Kissinger's real ambitions lay in the practice, not the study, of international relations. He used his Harvard position to meet major political figures and served as an advisor to leading Republicans, including Governor Nelson A. Rockefeller of New York and former Vice President Nixon. Kissinger's efforts won him only minor assignments under President John F. Kennedy, but when Nixon became president he appointed Kissinger as his national security advisor. Kissinger greatly overshadowed William P. Rogers, nominal secretary of state until August 1973, when Kissinger succeeded him, taking virtual control of U.S. foreign policy.

Kissinger's undoubted abilities included an immense capacity for hard work, a talent for grand designs and broad conceptualization, and the imagination to reformulate the international system to accommodate the relative weakness of the United States, de-emphasizing ideology in favor of a balance of power and the pursuit of closer relations with communist People's Republic of China (PRC) and détente with the Soviet Union. This resulted in the 1972 Strategic Arms Limitation Treaty (SALT) I and the Anti-Ballistic Missile Treaty that imposed limits on Soviet and American nuclear arsenals and delivery systems; the 1975 Helsinki Accords that normalized relations between Eastern and Western Europe and created the permanent Conference on Security and Cooperation in Europe (CSCE); and a rapprochement between communist China and the United States that Kissinger pioneered with a secret 1971 personal visit to Beijing. He also proved himself to be an excellent negotiator in complicated and protracted shuttle diplomacy designed to resolve longstanding Arab-Israeli tensions and disputes after the October 1973 Yom Kippur War.

Kissinger's weaknesses included a penchant for secrecy and intrigue, enormous vanity, and overweening personal ambition, all of which sometimes impelled him to decidedly unscrupulous behavior; an overriding concern to maintain international stability that often led him to endorse brutal right- or left-wing regimes; and a focus on realism in foreign policy to the near exclusion of all considerations of morality. The latter was apparent in his involvement in the secret bombing of Cambodia in the early 1970s, an operation that Congress halted when it became public in 1973, and the 1970–1971 invasion of that country despite Nixon's promise when he took office to end the Vietnam War as soon as possible; acquiescence in a 1973 military coup that brought the death of left-wing president Salvador Allende of Chile; endorsement of Indonesia's military takeover of Portuguese East Timor in December 1975 and the brutal suppression of indigenous resistance there; and readiness to authorize wiretapping against American bureaucrats suspected of leaking official information to the press. These aspects of Kissinger and his failure, constant negotiations notwithstanding, to end the Vietnam War—a conflict that his Cambodian policies effectively broadened—until 1973 made him the bête noire of many American liberals.

Conservative Republicans found equally opprobrious Kissinger's willingness to accommodate the communist Soviet Union and the PRC and, if Sino-American rapprochement required, to jettison the Republic of China (ROC, Taiwan), a longtime U.S. ally. Under Nixon's successor, Gerald R. Ford, who became president in August 1974 when the Watergate scandal forced Nixon's resignation, both SALT I and the Helsinki Accords on Europe that Kissinger helped to negotiate with the Soviets became targets for attack by such conservatives as California governor and presidential hopeful Ronald W. Reagan, who assailed the Soviet human rights record. The fall of Vietnam to communist forces in April 1975, little more than two years after Kissinger had negotiated the Paris Peace Accords supposedly ending the war, also damaged his credibility. On 3 November 1975 Ford replaced Kissinger as national security advisor, although Kissinger remained secretary of state until Ford left office in January 1977.

Upon leaving government, Kissinger established an influential business consultancy firm. He continued to provide unofficial advice to successive administrations, wrote and spoke extensively on international affairs, and published three weighty volumes of memoirs. He remains a perennially controversial figure. Liberals still denigrate his foreign policy accomplishments, and even decades later journalists including Seymour Hersh and, most notably, Christopher Hitchens argued that Kissinger's past behavior made him liable to trial and conviction for war crimes. It became almost an academic parlor game to point out discrepancies between Kissinger's own account of his time in office and the increasingly available documentary record. Outside the United States, Kissinger was a less polarizing figure, and as he began his ninth decade many in Europe and Asia still admired his achievements.